DDevelopment & Design

NoSQL devmeeting in Warsaw

I’ve spent this Saturday at NoSQL devmeetingin Warsaw, organized by Adam Lider, Piotr Zwoliński and lead by David de Rosier. At first I was reluctant to go, as my level of js mastery is clearly negative, and I have only theoretical knowledge about NoSQL databases, but as Maciej Próchniak noticed, these are exactly the reasons why I should.

The meeting started at 9am and lasted till 9pm (though I had to leave at 7pm), with one-hour break for lunch. David began with a gentle but fantastic introduction to CouchDB, MongoDB, Cassandra and Redis, after which we were split into groups of 3-4, each taking one of the databases aforementioned. Our task was simple: with four big MySQL (partitioned) dumps on the local SVN, we were to migrate the data to our NoSQL DB and then prepare a simple twitter application in any language we want, preferably javascript using Node.js. Our group took the hard way of playing with Node.js, easing it up with the choice of MongoDB (as it seems to have the best community and thus support). Node.js was more of an obstacle than help, mainly because of it asynchronous nature, but it’s quite possible that we just don’t know how to write good code in it. We definitely didn’t try much, being fine with “hey, it works!”, which is just right for the kind of hacking/prototyping we were into.

We had no problems with MongoDB. With Barack Obama’s 9 million followers in mind, we settled on the best model early, choosing eventual consistency and data duplication in the name of simplicity and query performance. Because I had to go two hours early, I’ve missed the part where we were to test the performance and try our luck with replication, but nonetheless this Saturday was clearly awesome. I loved the hackengarded at

33rd Degree, but devmeetings are even more fabulous. The formula is superb. If I were to add anything, it would be an open review of each application at the end. I’m really curious how other teams did it. Checkout devmeetings web page and if you have a chance to visit one, definitely go for it. It’s great, it’s free, and it’s one of the best ways to learn something useful fast.

Solution Architect @ TouK

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Need to make a quick json fixes – JSONPath for rescue

From time to time I have a need to do some fixes in my json data. In a world of flat files I do this with grep/sed/awk tool chain. How to handle it for JSON? Searching for a solution I came across the JSONPath. It quite mature tool (from 2007) but I haven't hear about it so I decided to share my experience with others.

First of all you can try it without pain online: http://jsonpath.curiousconcept.com/. Full syntax is described at http://goessner.net/articles/JsonPath/



But also you can download python binding and run it from command line:
$ sudo apt-get install python-jsonpath-rw
$ sudo apt-get install python-setuptools
$ sudo easy_install -U jsonpath

After that you can use inside python or with simple cli wrapper:
#!/usr/bin/python
import sys, json, jsonpath

path = sys.argv[1]

result = jsonpath.jsonpath(json.load(sys.stdin), path)
print json.dumps(result, indent=2)

… you can use it in your shell e.g. for json:
{
"store": {
"book": [
      {
"category": "reference",
"author": "Nigel Rees",
"title": "Sayings of the Century",
"price": 8.95
      },
      {
"category": "fiction",
"author": "Evelyn Waugh",
"title": "Sword of Honour",
"price": 12.99
      },
      {
"category": "fiction",
"author": "Herman Melville",
"title": "Moby Dick",
"isbn": "0-553-21311-3",
"price": 8.99
      },
      {
"category": "fiction",
"author": "J. R. R. Tolkien",
"title": "The Lord of the Rings",
"isbn": "0-395-19395-8",
"price": 22.99
      }
    ],
"bicycle": {
"color": "red",
"price": 19.95
    }
  }
}

You can print only book nodes with price lower than 10 by:
$ jsonpath '$..book[?(@.price

Result:
[
  {
"category": "reference",
"price": 8.95,
"title": "Sayings of the Century",
"author": "Nigel Rees"
  },
  {
"category": "fiction",
"price": 8.99,
"title": "Moby Dick",
"isbn": "0-553-21311-3",
"author": "Herman Melville"
  }
]

Have a nice JSON hacking!From time to time I have a need to do some fixes in my json data. In a world of flat files I do this with grep/sed/awk tool chain. How to handle it for JSON? Searching for a solution I came across the JSONPath. It quite mature tool (from 2007) but I haven't hear about it so I decided to share my experience with others.